Variable carrier system



Apl'll 1937- E. A. LAPORT VARIABLE CARRIER SYSTEM Filed Deb.

LEIAD llll m H.F. SOURCE A.F. SOURCE P1E-E INVENTOR. Edmund A. LBPUII fiM X an an .rzmmmju b31540 ATTORNEY.

' SUPPRESSDRjELEETRUDE VOLTAGE Patented Apr. 13, 1937 UNITED STATESPATENT OFFICE VARIABLE CARRIER SYSTEM tion of Delaware ApplicationDecember 24, 1935, Serial No. 55,978

3 Claims.

This invention pertains in general to radio transmission systems andspecifically relates to the transmission of modulated high frequencyenergy.

One of the objects of my invention consists in providing a radiotransmission system having means for producing modulated high frequencyenergy with the level of the carrier frequency varied in accordance withthe level of the modulation energy.

A further object of the invention comprises providing a variable carriertransmission system having a transmitter with a source of high frequencyoscillations modulated by a source of modulation energy to producecarrier and side band modulated high frequency energy, the highfrequency energy in the range of the carrier being varied in magnitudein accordance with the level of the modulation energy.

These and other objects will be apparent from the following, referencebeing had to the accompanying drawing in which:

Fig. 1 is a diagrammatic representation of one embodiment of theinvention; and

Fig. 2 is a graphical representation of relative dynamic zones of theoperating characteristics which are employed in the system of Fig. 1.

This invention contemplates a radio transmission system for transmittingmodulated high frequency energy to a radio receiver whereby the highfrequency energy in the carrier frequency range is supplied to thereceiver only in proportion to the magnitude of the modulation energy.That is, low values of modulation energy or audio signal will betransmitted by carrier frequency energy of low magnitude whereasmodulation energy of a high level will be transmitted by carrierfrequency energy of a corresponding high level. In accordance with theinvention, plural electrode tubes are employed in a balanced circuitenergized by a high frequency source and an audio frequency source forproducing modulated high frequency energy. Further connections areprovided for controlling the tubes from a rectifier-amplifier systemwhich is controlled, in turn, by the audio frequency modulation source.

Referring to the drawing in detail, a high frequency source I isconnected to the primary winding of transformer 2 having secondarywindings 3 and 4. This high frequency source comprises means known inthe art for producing sustained high frequency oscillations of afrequency suitable for carrier frequency transmis-' 55 sion purposes. Apair of pentode electron tubes and 6, of which the Type 59 is anexample, are provided with their control electrodes respectivelyconnected to the windings 3 and 4 in a balanced arrangement as shown. Asource of biasing voltage 1 is provided in circuit with the midpoint ofwindings 3 and 4 and the cathodes of the tubes 5 and 6.

The screen electrodes of the tubes 5 and 6 are connected in parallelwith a rectifier tube I0. Suppressor electrodes II and ii. are connectedthrough the secondary winding [3 of a transformer 4 and thence through asource of biasing voltage iii to the ground potential cathodes of thetubes 5 and 6. The anodes of the tubes 5 and 6 are respectivelyconnected to primary windings i7 and I8 of a transformer IS. Themidconnection of these windings H and 18 includes a connection to asource 2| which supplies constant. positive anode potential. Thesecondary winding of transformer I9 includes a connection to a load 22.The load 22 is representative of any form of utilization circuit, suchas a wired radio or space radio transmitting arrangement.

An audio frequency source 24 is provided with connections to the primarywinding 25 of transformer M. The source 24 is representative of anysuitable means for providing modulation or signalling energy includingvoice currents suitable for program purposes. This source 25 alsoincludes a connection to the primary winding 261 of a transformer 21having a secondary windingv 28. Secondary winding 28 includes aconnection directed through an electron tube linear amplifier 29 andthence through a balanced transformer 30 to the double Wave rectifierunit I 0.

The positive terminal of the rectifying circuit comprising transformer30 and double diode I0 is connected to the screen electrodes of pentodes5 and 6. Condenser 9 serves as a smoothing filter, so that the screenpotential variations are reduced to syllabic or modulation envelopeform. The rectifier output is dissipated in the screen circuit, thelatter constituting the rectifier load circuit of sufficiently highimpedance so as to give a virtually linear relation between platevoltage applied to the two plates of the diode l0 and screen current.The circuit is designed to provide for adequate power capacity in theamplifier 29 and rectifier In to fully energize the screen circuitwithin the desired ranges of operation.

Referring to Fig. 2, the solid lines show the relationships betweenoutput current into a load circuit, screen potential and suppressorpotentials. The data here represented are obtained in connection withthe circuit of Fig. 1, with a constant zero load current when the screenpotential is. zero, and bias source is adjusted to this value.

Such a choice is indicated by dotted line 3!. It will befnoted that thisline traverses theseveral 15 screen-voltage output-current curves atvery nearly the middle of their most linear'portions. In the operationofthe system modulation voltages are applied to the suppressorelectrodes,and

maximum degree of linearity is effected betweenoutput current andsuppressor voltage;

In accordance with the invention, when there isno modulation energy fromsource '24, and the screen voltage from rectifier l0 retains a virtuallylinear relationship with modulation voltage appliedto the suppressorelectrodes II and I2, an adjustment is made which brings thescreen-voltage suppressor-voltage operating zone within the boundariesof the lines 33 and 34 with point 32'as the static origin. By changingthis adjustment,

7 the suppressor-voltage variations may be made to occupy the muchlarger zone of operation between lines 35 and .36, or any intermediatearea. In program operation, the screen voltage varies at the syllable orenvelope rate, while the suppressor voltage follows the instantaneousprogram signal variations precisely. For this reason, preliminary.circuit adjustment is made, using a constant signal from source 24, tobring the operation of the circuitwithin the zone of lines 33 and 34,and when typical program signals are supplied from source 2 4, theinstantaneous suppressor voltage varia- 'tions may swing out to thelimits of the zone lying between lines 35 and 36 without distortion dueto overmodulation.

v Bias source I is adjusted to a value which brings the anode current ofelectron tubes 5 and .6 to nearly zero when full operating anode andscreen electrode potentials, as well as proper operating value ofsuppressor bias voltage from source 15,

50. are .applied'in the absence of excitation from source .I; Followingthis, excitation from source I applied until an operating voltage whichhas a peak Value at least equal to that of bias voltage 1 has beenreached. The circuit is then in con- 55 dition to perform in accordancewith Fig. 2.

' The foregoing provides a system for the production and transmission ofmodulated high frequency energy in the form of modulation side bandfrequencies with a carrier frequency, the level of the carrier frequencybeing variable in accordance with the magnitude of the modulation energyavailable for transmission purposes. Although there has been disclosed apreferred form of the system, it will be understood that variousmodifications and changes ,can be. made without departing'from theintendedscope of the invention. I do not, therefore, desire to' limitmyself .to the foregoing exceptas'may be pointed out in the appendedclaims.

What Lclaim' as new and original and desire to secure by Letters Patentof the United States is: 1. A variable carrier transmission systemcomprisingja pair'of electron tubes each includinga cathode, a controlelectrode, a screen electrode, a

T suppressor electrode and an anode, a balanced input circuit includedbetween the control electrodes and the cathodes of said tubes, means forsupplyingsustained high fre'quencyoscillations tosaidinput circuit,amodulation circuit included between the suppressor electrodes and thecathodes of said tubes, a source of modulation energy for energizingsaid modulationacircuit, a balanced output circuit included between theanodes of said tubes, a load.v circuit energized by said output circuit,a double wave rectifier system 'operatively energized solely .by saidmodulation energy, and connected with said screen, electrodes forimpressing unidirectional potentials upon the same, a smoothingcondenser so includedin said'rectifier system as to reduce thepotentials applied to said screen electrodes to syllable envelopeformand a circuit extending betweensaidsource :of modulation energy and saidrectifiersystem for supplying'modulation energy thereto, said'highfrequency source and said source of modulation energy operating saidtubes to produce modulated high frequency energy with modulationsideband frequencies-and acar- V rier frequency, andsaidrectifler systemcontrolling said tubes through rectified modulation frequency voltagesapplied to said screen electrodes to vary the output energy level of:said "carrier frequency in accordance with. the envelope form of saidmodulation energy.

f2. 'Ifhe'system in accordance claim l in which said rectifier systemincludes an amplifier for amplifying the modulation energy from thelevel availablefor said suppressor electrodes to a, higherlevel-available for, rectification. to energize saidscreen electrodes.

;3. The system in accordance "with claim ,1 in V which saidscreenelectrodes .are connected in parallel and in which said suppressorelectrodes are also connected in parallel.

w EDMUND A. LAPORT.

